1. Field of the Invention
The present invention pertains to a semiconductor device having nickel silicide and a method of fabricating nickel silicide. The semiconductor device has nickel silicides including nickel monosilicide and nickel disilicide on the surface of source/drain regions, and the nickel silicides are formed by two rapid thermal processes.
2. Description of the Prior Art
Silicide has been widely applied to IC fabrications for its advantages, such as high melt point, low resistance, etc. Currently, while critical dimension, contact area, and junction depth are diminished gradually, the gate and source/drain regions of most semiconductor devices require silicide to reduce gate resistance, contact resistance, and RC delay, so as to improve drive current.
Silicide is fabricated by first forming a metal thin film on a semiconductor substrate, and subsequently performing a thermal process. Generally, the metal thin film is formed by, for instance evaporating or sputtering, on the semiconductor substrate covering where to form silicide such as gate, and source/drain regions. Thereafter, the semiconductor substrate is heated so that the metal thin film reacts with the gate and source/drain regions.
Silicide has another advantage of self-alignment. Currently, self-aligned silicide (also referred to as salicide) has been broadly applied in IC fabrications. Please refer to FIG. 1 through FIG. 4. FIG. 1 through FIG. 4 are schematic diagrams illustrating a conventional method for fabricating silicide. As shown in FIG. 1, a semiconductor substrate 10 is provided. The semiconductor substrate 10 includes isolations 12 (e.g. field oxide or STI), a gate dielectric layer 14, a polycrystalline silicon gate 16 disposed on the gate dielectric layer 14, a spacer structure 18 formed alongside the polycrystalline silicon gate 16, and source/drain regions 20 disposed in the semiconductor substrate 10 between the polycrystalline silicon gate 16 and the isolations 12.
As shown in FIG. 2, a physical vapor process is performed to deposit a metal thin film 22 on the semiconductor substrate 10 covering the polycrystalline silicon gate 16 and the source/drain regions 20. As shown in FIG. 3, an anneal process is performed to react the metal thin film 22 with the polycrystalline silicon gate 16 and the source/drain regions 20, so as to form silicides 24 on the polycrystalline silicon gate 16 and the source/drain regions 20. As shown in FIG. 4, the unreacted metal thin film 22 is removed.
Normally, metal materials for fabricating silicide are titanium, cobalt, nickel, etc. Titanium disilicide (TiSi2) has a lower resistance ranging between 12 and 20 μΩ-cm, however, it suffers from narrow linewidth effect. When critical dimension reduces to less than 180 nm, the sheet resistance increases dramatically. Therefore, cobalt disilicide (CoSi2) and nickel monosilicide (NiSi) whose resistances are slightly higher (15 to 20 μΩ-cm) are more suitable for forming silicide because nearly no narrow linewidth effect is observed. Between these two materials, nickel consumes less silicon in the silicidation process, and thus is more preferred.
Nickel silicide, however, still suffers some disadvantages. Please refer to FIG. 5 and FIG. 6. FIG. 5 and FIG. 6 are schematic diagrams respectively illustrating a semiconductor device having nickel silicide formed by a conventional method. As shown in FIG. 5, the semiconductor device includes a semiconductor substrate 30, isolations 32, a gate dielectric layer 34 disposed on the semiconductor substrate 30, a polycrystalline silicon gate 36 disposed on the gate dielectric layer 34, a spacer structure 38 formed alongside the polycrystalline silicon gate 36, and source/drain regions 40 positioned in the semiconductor substrate 30 between the polycrystalline silicon gate 36 and the isolations 32. Nickel silicides 42 are formed on the surface of the source/drain regions 40. However, the nickel silicides 42 of the semiconductor device (especially a P type device) tend to grow downward as shown in FIG. 5. This phenomenon is referred to as spiking effect, and leads to current leakage between the source/drain regions 40 and the semiconductor substrate 30. In addition to the spiking effect, the nickel silicides 42 of the semiconductor device (especially an N type device) tend to grow laterally as shown in FIG. 6. This phenomenon is referred to as piping effect, and results to reduction of threshold voltage.
In view of the aforementioned problems, the present invention proposes a semiconductor device having nickel silicide and a method for fabricating nickel silicide to avoid these problems. The nickel silicide of the present invention includes nickel monosilicide and nickel disilicide formed by two rapid thermal processes. Consequently, spiking defect and piping defect are prevented.